[PHI Decoupling] remove "paddle/fluid/platform/float16.h" and "paddle/fluid/platform/for_range.h" in phi. (#47817)

* rm "paddle/fluid/platform/float16.h" in phi

* rm "paddle/fluid/platform/for_range.h" in phi

* support pure bfloat16

* support bf16 linear

* update PR to pass CI

* tiny fix where_grad_kernel.cu

* add bfloat16 to selu_grad to pass CI

* fix selu grad compilation error

* tranfer the selu_op and pass the CI

* add sig files

* fix code

* fix by code review

* remove TOOD

* change the include position

* change the head position